1. Field of the Invention
The present invention relates to sealing devices for enclosures and more particularly to enclosures that seal or attenuate electromagnetic radiation, including RF radiation, sound, blast, gas and other environmental conditions.
There are numerous situations in which it is desirable to have an enclosure sealed from outside or inside for radio frequency or other electromagnetic radiation and conditions. In particular, in the testing of electrical apparatus it is necessary to have the equipment isolated from outside radiation and in such cases, enclosures are provided for the equipment under test. In other cases such as the transmission of information by electronic means, it is desirable to shield the apparatus from possible outside surveillance and in such cases radio frequency shielded enclosures are used.
A critical part of such enclosures is the doorway or other accesses which are opened to permit egress and ingress of persons or apparatus. The present invention is directed to an access construction (door) that is especially convenient and which provides an improved sealing of electromagnetic radiation.
2. Description of the Prior Art
Numerous shield system door constructions have been designed most of which provide hinged doors that close against a door frame and provide a slot on the frame and a plate on the door. When the door is closed the plate fits within the slot and a sealing strip is located within the slot to effect a radiation seal. Examples of this type of structure are shown in U.S. Pat. Nos., 3,589,070 and 4,069,618. The sealing element within the slot comprises a resilient strip of fingers that are secured within the slot and bear against the plate when the door is closed. This type of construction presents various disadvantages such as the bending and breaking of the various fingers and a certain leakage of electromagnetic radiation through the door seal.
Another type of construction contemplates an inflatable member within a slot-plate type door and frame in which the member is inflated to effect a seal. Examples of this type of construction are shown in U.S. Pat. Nos. 3,604,834 and 4,371,175 and 4,399,317.
As noted above, the typical door construction for electromagnetic sealed enclosures are hinged. An example of a sliding door is shown in U.S. Pat. No. 3,604,834 which employs an inflatable bladder in an attempt to effect a seal.